Field of the Invention
The present invention relates to an engine control device, and more particularly to an engine control device which performs a catalyst early warming control for accelerating warm-up of a catalytic device provided on an exhaust gas passage.
Description of Related Art
Conventionally, in a spark-ignition engine, in order to accelerate warm-up of a catalytic device provided on an exhaust gas passage, a technique referred as AWS (Accelerated Warm-up System) has been implemented. The AWS is a technique for accelerating warm-up of a catalytic device, in a situation such as immediately after an engine cold start and the catalytic device is not in an activated state, for example, by increasing the intake air amount and retarding the ignition timing beyond the compression top dead center than in a case when the catalytic device is in an activated state under the same operating state (for example, idling operation), to thereby cause afterburning of fuel-air mixture even during the expansion stroke so as to increase the exhaust gas temperature and eventually the exhaust gas heat quantity (for example, refer to Patent Document 1: Japanese Laid-Open Patent Publication 2014-136989A). More specifically, Patent Document 1 discloses that injected fuel is split into two parts (split injection) to form a weak stratified charge state in a combustion chamber so as to generate weak stratified charge combustion, in order to suppress degradation of the combustion caused by the retardation of the ignition timing in executing the AWS as described above. Here, the weak stratified charge state corresponds to a state where the fuel-air mixture in the combustion chamber becomes relatively rich in the vicinity of an ignition plug (particularly, in the vicinity of an electrode of the ignition plug), and becomes relatively lean around such area (weak stratification of the fuel-air mixture inside a cylinder).